Home wireless networks or PANs (Personal Area Networks) are conventionally designed to interconnect communications devices or “network devices”, for example digital instruments, telephones, personal digital assistants, speakers, television units, multimedia players situated in proximity to the user. The range of such a communications network is about a few meters.
Even though home networks may be wired, use of a wireless medium is still increasing, which refers to wireless home network or wireless personal area network (WPAN).
The Bluetooth (IEEE 802.15.1), UWB, ZigBee (IEEE 802.15.4), IEEE 802.11e or IEEE 802.15.3 standards are nowadays among the most widely used protocols for wireless communications networks.
The radio transmission systems implemented in these networks currently use a wide range of transmission frequencies, for example 2.4 GHz, 5 GHz and 60 GHz. These frequencies are particularly well suited to data transmission at very high bit-rates over a limited range, for example as a means of connectivity between the different parts of a “home cinema” type communications network.
However, these systems are very sensitive to interference and shadowing phenomena due to the presence of an unexpected obstacle. This generally results in data losses on the communication path between a sending network device and a receiving network device, where the obstacle is located.
In order to overcome data loss, several remedies have been developed. In a first one, the sending network device may repeat the transmission of one piece of data several times. This however reduces its overall transmission bit rate.
In another remedy, relaying network devices may be used in conjunction with the sending network device to provide alternative communication routes or paths, and thus to increase the probability that the receiving network device correctly receives the data. Relaying network devices are well-known by one skilled in the art.
This method involving relaying network devices is usually referred to as a mesh communication method or relay-based communication method depending on whether one or all the network nodes play an active role in determining the strategy of routing/relaying data.
Because such a relay-based communication method requires transmitting the same data several times on the wireless network (from the sending network device to a relaying network device, and then from the relaying network device to the receiving network device), it is preferably used for applications requiring low bandwidth, such as for transmitting control data or command data, or even applications based on audio data communication.
The relay-based communication mode of the wireless network operates according to a relay scheme that defines one or more communication routes between pairs of sending and receiving network devices and also defines allocation of the network medium accesses to the network devices.
The routes may be a single transmission link between the sending network device and the receiving network device, or may involve one or more relaying network devices between them, i.e. several transmission links.
As known by one skilled in the art, the routes are usually stored in routing tables spread over the network.
On the other hand, applications requiring high bandwidth, such as video applications, should not be handled with such method, since this would require compressing the video data, and thus decreasing the video quality.
Given the amount of data for videos, it is desirable to send them only once over the network. This is achieved by only using the transmission link between the sending network device and the receiving network device, without using relaying network devices.
Several potential communication paths exist for the transmission link between the sending network device and the receiving network device, including a direct communication path, also referred to as line-of-sight or LOS path, and indirect communication paths, also referred to as non line-of-sight or NLOS paths.
In the case of NLOS paths, a relaying of the data is obtained though reflection of the radio signal on walls, objects or obstacles.
The receiving network devices are configured to handle the several copies of data that may be received due to multiple reflections on obstacles, to process only one entire copy.
Such a method involving solely the transmission link between the sending and receiving network devices is referred as a point-to-point communication method.
Both the relay-based communication method and the point-to-point communication method may be implemented in the same wireless communications network.
One may note that the relay-based communication method enables two widely separated network devices to communicate, which could not communicate in a point-to-point communication method due to the long distance between them exceeding for example their transmission/reception range.
The several communication paths, either LOS or NLOS paths, may advantageously be used to set up the sending and receiving network devices (including the relaying network devices since they act as sending and/or receiving devices), in particular regarding their antenna configuration. This is because phase array antennas, also referred to as smart or agile antennas, may be easily configured to match specific communication paths.
A network device may adapt its antenna configuration dynamically according to its operating mode, either a relay-based communication mode or a “point-to-point” communication mode.
This tends to improve the bit error rate for the communications in particular when the network device operates as a receiver.
An illustration of this is the case of a receiving network device that uses a directive antenna pattern, i.e. an antenna with a narrow detecting angle, to receive data from a sending network device that uses a quasi-omni directional antenna pattern, i.e. with a large transmitting angle. In this case, the receiving network device is highly sensitive to any shadowing phenomena that may occur in the communication path linking it to the sending network device, given the narrow detecting angle. Therefore, it is advantageous for the receiving network device to adapt its antenna pattern so as to receive data from a direct or an indirect communication path, depending on the actual level of perturbation of these communication paths.
Publication FR 2 937 822 discloses a method for monitoring a perturbation level of several communication paths to detect and locate the presence of an obstacle causing shadowing in the network coverage area.
In the relay-based communication mode, the efficiency of the network may greatly vary depending on the presence of one or more moving or mobile obstacles in the network coverage area.
Increasing the number of relaying network devices for the same sending network device does not appear to be an appropriate solution, since this would increase the number of times the network is used to relay the same data. This would result in a significant bandwidth overhead and a decreased overall transmission bit rate.
In this context, several other solutions have been provided, such as the method disclosed in publications FR 2 939 271 and FR 2 939 267.
In publication FR 2 939 271, the quality of the communication paths for each receiving network device is monitored to evaluate the receiving capacities of the devices and then the impact of a mobile obstacle on them. The communication routes of the network are thus adapted according to the receiving capacities of the devices, when the impact is considered as critical.
This method has drawbacks. In particular, due to monitoring the whole network coverage area, the network devices level perform unnecessary extra processing since most of the monitored communication paths are not actually perturbed and/or are not used for locating the mobile obstacle.
In publication FR 2 939 267, the quality of a communication path in a perturbed area where an obstacle has been located, is monitored in order to evaluate an absorption level by the obstacle and determine whether the obstacle is a human being. In the affirmative, a security area is defined around the perturbed area, and communications routes are adapted to avoid crossing the security area when using a directive antenna pattern for transmitting.
This method aims at protecting humans from high power electromagnetic radiations.
This management method also suffers from drawbacks.
In particular, it requires extra processing by network devices: a first operation has to be implemented in each network device to monitor the perturbation level of the communication paths so as to determine any perturbed area; and a second operation has to be subsequently implemented in particular network devices to evaluate the absorption level of the obstacles.
There is therefore a need to lighten the processing load on the network devices for tracking the mobile obstacles while appropriately adapting the routing in the network.